The best weapon for the SS is probably the spiked chain and the OA Samurai nabs the Ancestral Daisho ability and a bonus feat. This will allow you to make better use of some of the treasure you find if you can convince your DM to allow you the Spiked Chain as your ancestral daisho. If you’re a two weapon fighter, try a 2 level dip in either fighter or ranger to pick up 2 weapon fighting and other goodies.

I think human is a very strong choice, but many small races are excellent choices also since the SS doesn’t rely on strength to deal damage. The whisper gnome is EXTREMELY saucy. Most of the Halflings can be excellent choices also, and the Water Halfling, if that racial variant is available, is a particularly good choice.

If you’re playing a small race, I’d swap the 12 in Int with the 10 in Str so you can still carry a haversack full of goodies without difficulty.

We need to take maximum advantage of the Shadow Blade feat, so expect to stay mostly in Assassin’s Stance once you have access to it.
1 – Hunter’s Sense – Gives Scent, situationally useful. Notable interaction with Track if you’re a ranger also!
1 – Child of Shadow – Mainly to use Shadow Blade
3 – Assassin’s Stance – yay, we’ll spend a lot of time in this one
5 – Hearing the Air – You never know when you might need blindsense and a bonus to listen checks
8 – Balance on the Sky – Probably won’t be using it in combat due to the “one hand free” clause, but can be extremely useful.

Have a blast! You've got reach, a number of excellent strikes, several solid boosts and teleportation effects, and a number of useful counters. Between tumble, quicksilver motion and your teleportation abilities you should be able to move around the battlefield more or less at will, and land a devastating strike every round for your standard action! Your job is to let the big scary guys in the party draw the heavy fire while you dance around the battle scoring decisive hits. Alternatively, you make an excellent scout as you're able to defend yourself, stay unnoticed, make quick escapes, and deal decisively with unprepared enemies.

As far as saves go, I would always keep Mind Over Body prepared to dodge poisons and nasty save-or-suck/dies aimed at your fort save. If you know you're going up against magic users, it may be wise to swap one of your strikes to keep Moment of Perfect Mind prepared also to buffer your will save.